Video printers are widely used for printing onto a photosensitive sheet images digitally processed and displayed on a display. Printing methods for video printers include thermal method, ink-jet method, laser beam scanning method, and liquid crystal shutter method. Of these methods, the optical printer method, wherein the image is formed by exposure of a photosensitive medium with light from a light source under exposure timing controlled by a liquid crystal shutter, has attracted attention for its suitability to compact, lightweight designs. Prior art examples of such optical printer method are disclosed in Japanese Laid-Open Patent Application 2-287527 and 2-169270.
The prior art examples cited above will be described referring to FIG. 16. In FIG. 16, a casing 11 houses a film loading section 12 that contains a film pack FP containing a plurality of sheets of self-processing film F, each being a photosensitive medium. Located adjacent to the opening 13 of the film loading section 12 is a set of transport rollers 16 comprising a pair of rim drive rollers 14a and 14b for drawing out by gripping therewith a predetermined single sheet of film F, which has been exposed, from the film pack FP housed in the film loading section 12 and a pair of ironing rollers 15a and 15b for developing the exposed film F.
An exposing and recording section 17 for producing the image on the film F is disposed between the rim drive roller pair 14a and 14b and the ironing roller pair 15a and 15b. The exposing and recording section 17 includes a light source 18 such as a halogen lamp, and is designed so that the film F is exposed to the light from this light source 18 through an optical fiber bundle 19, color filters (not shown) of three colors (RGB) disposed parallel to the image auxiliary scanning direction, a liquid crystal light valve 20, and a gradient index lens array 21.
A polarizing plate is disposed above and below and to the sides of the liquid crystal light valve 20 with the direction of polarization thereof oriented parallel. A first glass substrate is disposed to the inside of the polarizing plate, one face of this first glass substrate being provided through vacuum evaporation with thin films consisting of coloring matters of three different colors (R, G, and B) that serve as color filters (not shown). The other face is provided with transparent electrodes arranged along the color filters (not shown), i.e., a plurality of pixel electrodes disposed in linear fashion in the auxiliary scanning direction.
Liquid crystals such as twisted nematic liquid crystals are sealed between the pixel electrodes and a second glass substrate. At the interface of the second glass substrate with the liquid crystals, a common electrode, being a transparent electrode, is produced through vacuum evaporation at the side of the second glass substrate. The aforementioned polarizing plate is located on the other side of the second glass substrate; light passing through this polarizing plate is directed through the gradient index lens array 21 for the exposure of the film F.
The prior art described above, however, lacks means for accurately controlling the relative motion of the photosensitive medium and the exposure light, and thus has the drawback of image distortion caused by deviation in the speed of relative motion of the photosensitive medium and the exposure light.
Accordingly, it is an object of the present invention to provide an optical printer apparatus that overcomes the aforementioned drawbacks of optical printer apparatuses of the prior art, by assuring a constant relative motion speed of photosensitive medium and exposure light over the entire scanning area, thereby affording images that are free from distortion.
It is a further object of the present invention to provide an optical printer apparatus equipped with a head support structure capable of stably supporting over the entire scanning area the optical head that emits the exposure light.